I've seen lots of things! Did you see there's a new Japanese client incoming? (Separate from Korea and Global app.) I think this is my biggest discovery since, AFAIK, it has not been announced. And yes all packets are encoded after the first, however since they don't use asymmetric key encryption you can MITM as much as you want as long as you successfully emulate the block cipher they use. I will do a write-up about it when I get a chance.
Are you using the Nexon API or in-game packets? I can help with either. I think you can get a lot more information from in-game packets, I have a clientless in-game setup so let me know if you need help achieving something similar.